Natural cereal products have in recent years achieved a high degree of consumer acceptance, and in some cereal products employ whole grain particles as the basic or sole ingredient. In the evaluation of any cereal grain product, whether whole grain, milled, or flaked, several factors must be considered iin evaluating the end consumer product. These factors in large part relate to the sensory qualities required of food commodities in the market place and include considerations regarding shelf stability, organoleptic attributes and consumer convenience. Consumer convenience primarily includes ease of preparation of the final food product, while the organoleptic attributes of the food product include its appearance, aroma, flavor and texture in both the final ready-to-eat form and the unprepared form, that is, the form in which the consumer receives the product.
Shelf stability involves the capability of the product, as presented to the consumer, to remain in a desirably consumable form or ready to prepare during the period of time required for delivery to the consumer and sufficient time thereafter until consumption. In the case of grain products, shelf stability is reliant chiefly upon the suppression of enzymatic and oxidative reactions which may occur within the grain. When such reactions are allowed to go forward, the grain becomes rancid. In particular, enzyme or lipid levels are more prominent in oat grains than other grains. Enzymatic reactions, particularly lipolytic reactions, occur relatively slowly at low moisture levels and temperatures and, unless inactivated or removed, can cause rancidity by the production of high levels of free fatty acids which can subsequently break down into peroxides. All samples of raw undamaged oat kernels, as harvested, contain 3-10% of their fat already in the form of free fatty acids (FFA). In the normal storage of unmilled raw oats, e.g., at 13% moisture content and 18.degree. C., FFA levels increase slowly. If the oats are crushed, production of FFA can increase dramatically. The rate of such increase is generally accelerated by high moisture content and higher temperatures. The development of a high level of lipase activity in this manner, though not significant in a nutritional or healthful context, can render oat grain unsuitable for human consumption, though such rancid grain may be fed to animals.
Oat grain has been found to have its own antioxidant properties which can provide limited protection for the grain under some conditions. In fact, oat flour itself has been used as an antioxidant under the trademark "Avenex" for extending the shelf life of food products by treating with "Avenex" or wrapping the product in paper so treated. In spite of such natural antioxidant properties, rancidity of oats attributable to oxidation can occur under conditions of high heat and low moisture, and may be typified by an increase in free fatty acids as well as subsequent high peroxide levels. The occurrance of both enzymatic and oxidative rancidity of oats can be observed through a deterioration of the organoleptic attributes, most notably in the aroma and flavor of the grain.
The preparation of a whole grain product encounters significantly greater problems in reaching the necessary shelf stability when compared with the identical grain product in cut or flake form. In the whole grain form, efficient heat treatment of the grain is more difficult to achieve than that of cut or flaked grain products, which have a much higher surface area per grain particle and can reach a desired temperature quicker and more consistently on the application of a given amount of heat. In addition the moisture content of the cut or flaked grain may be released more easily. Thus, it is possible to use lower temperatures for longer periods of time to inactivate the enzymes within cut or rolled grain particles. Because the lower temperatures may be used, there is little or no danger of oxidation and yet the enzymes can be completely inactivated. In rolled grain products, such as rolled oats, the exterior bran layer is cracked and the kernel exposed; the moisture content of the grain is thus more easily controlled and the grain can be more uniformly heated. However, the whole grain oat with its bran layer intact retains its moisture longer on heating, thereby keeping the interior temperature of the grain significantly lower than its exterior temperature for longer periods of time. Thus higher exterior temperatures are required to inactivate the enzymes and for the desired drying effect to occur. With such higher temperatures comes an increased probability that oxidation will occur and promote rancidity, though the enzymes may be completely inactivated.